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Difficulty: HardOSPFv2 Network Types and DR/BDR Selection

A network administrator executes the `show ip ospf interface GigabitEthernet0/1` command on router R1 connected to an enterprise Ethernet segment, yielding the following operational output:

text
GigabitEthernet0/1 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 1, Router ID 10.10.10.1, Network Type BROADCAST, Cost: 1
State DR, Priority 1
Designated Router (ID) 10.10.10.1, Interface address 10.10.10.1
Backup Designated Router (ID) 10.10.10.2, Interface address 10.10.10.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

If the administrator modifies the OSPF interface network type on all routers attached to this segment by executing the `ip ospf network point-to-point` command, which two operational changes will take effect on this interface? (Choose two.)

  1. OSPF will completely bypass the election of a Designated Router (DR) and Backup Designated Router (BDR) on the interface.Answer
  2. Neighbors will continue to dynamically form adjacencies using 224.0.0.5 while maintaining the default 10-second Hello and 40-second Dead timers.Answer
  3. C
    The default OSPF Hello timer will automatically adjust to 30 seconds and the Dead timer to 120 seconds to reduce multicast overhead.
  4. D
    Dynamic neighbor discovery via multicast will be disabled, requiring manual configuration of static OSPF neighbor statements.
  5. E
    A router configured with an OSPF interface priority of 0 will be unable to establish a FULL neighbor adjacency on the link.

Answer

Reconfiguring the Ethernet interface to an OSPF point-to-point network type eliminates DR/BDR elections entirely while retaining dynamic multicast neighbor discovery (224.0.0.5) with 10-second Hello and 40-second Dead timers.
Changing an OSPF interface from broadcast to point-to-point disables DR and BDR elections because the link is assumed to connect exactly two routers. Additionally, point-to-point network types retain dynamic neighbor discovery via multicast (224.0.0.5) using standard 10-second Hello and 40-second Dead timers.

Step-by-Step Solution

1
Analyze the default OSPF operational traits for the BROADCAST network type.
The BROADCAST network type elects a DR and BDR and uses default timers of 10s Hello and 40s Dead with multicast address 224.0.0.5.
Ethernet interfaces default to BROADCAST network type in Cisco IOS.
2
Evaluate the impact of changing the interface network type to POINT_TO_POINT.
POINT_TO_POINT network types do not elect DR or BDR roles because only two nodes reside on the segment.
DR/BDR elections exist solely to reduce adjacency counts on multiaccess media.
3
Determine timer and neighbor discovery behaviors for POINT_TO_POINT mode.
POINT_TO_POINT retains dynamic neighbor discovery using multicast (224.0.0.5) and keeps the 10s Hello / 40s Dead timer values.
Timers only change to 30s/120s on non-broadcast or point-to-multipoint OSPF network types.

Key Concept

OSPFv2 Network Types (Broadcast vs. Point-to-Point) and DR/BDR Election Rules
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Topics

OSPFv2 Network Types and DR/BDR Selection

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